The invention is based on a discharge system for volatilized fuel as generally defined hereinafter. Such discharge systems are used to carry fuel components that have been volatilized from the fuel sources of the engine, for instance the fuel tank or a carburetor float chamber, to the engine where they can be burned, rather than into the open air. A discharge system is already known in which the introduction of volatilized fuel via the delivery system is interrupted during engine idling, to prevent excessive enrichment of the fuel-air mixture, which would cause undesirable engine operation. To this end, a pneumatic control line is connected to the delivery regulation valve and leads to the intake tube in the immediate vicinity of the throttle valve. An electromagnetic switching valve is disposed in the control line and opens the control line to the atmosphere whenever the temperature in the fuel container becomes too high. This kind of discharge system is not only expensive, but it does not allow optimal regulation, in accordance with engine operating characteristics, of the amount of volatilized fuel fed to the engine.